Problems encountered when installing Oracle by myself.
1. When logging in to sqlplus, it prompts that the password is incorrect.
When I first reinstalled, I used regular uppercase and lowercase letters and numbers. When I reinstalled again, I used 123456, so that sqlplus can log in normally (there should be some settings that can solve it directly)
2. Find the oracle data creation method.
Because mysql needs to create the library before creating the table. Oracle will let you create the library when you install it. So when operating Oracle, we operate in one of the libraries. 
3.sql developer failed to connect to oracle.
As shown in the picture:
The error reported is: Status: Failed - Test failed: Listener refused the connection with the following error:
ORA-12505, TNS:listener does not currently know of SID given in connect descriptor
Obviously the SID is wrong. There is no sid setting in the installation database. When searching online, it says: the default sid is ex. I reinstalled Oracle and confirmed that there is still no place to set the sid. I found this when I created new oracle data:
It turns out that the default is the name of the database. Then I modified the previous sid, and the sql developer connection was successful (I later discovered that the connection name can be written casually)
